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7/28/2019 Lecture01 Week 01

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Lecture NotesWeek 1

ChE 1008

Spring Term (03-2)


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Lecture 1


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Staged Separations


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Equilibrium Staged Separations

What do we mean by separations?

What do we mean by equilibrium?

What do we mean by staged?

That is what is this course about?


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Overview of the Overview

This course covers the basic work horseseparation methods most commonly usedin the chemical and petroleum industry

Distillation Absorption

Extraction

It does not cover newer advancedseparations methods: Adsorption (e.g., PSA) Note the difference: AB

vs. AD

Membrane separation

Electrophoresis


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Overview of the Overview

You will also learn basic problemsolving skills: 0. I want to and I can

1. Define the problem 2. Explore or think about it

3. Plan

4. Do it

5. Check

6. Generalize


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Separations Distillation


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Staged Separations Distillation


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Staged Separations McCabe-Thiele Method

Chapter 2

EquilibriumChapters 3 & 5

Flash & Feed

Chapters 4 & 5

Mass Balances

Chapters 5 & 6

Stage Solution


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Separations Distillation Design

Chapters 7 & 9

Multicomponent

Distillation

Chapter 12

Design


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Separations Why Needed?

Separations are employed in chemical plants wherethe separation of a mixture is required to obtain arelatively pure chemical species.

Separations are usually closely integrated with other

unit operations in the process flow, obtaining feedsfrom other unit operations and separating the desiredproduct or providing the required product streams forfeed to other units.

The number of other unit operations is often smallcompared to the number of unit operations involvingseparations it is often relatively easy to makesomething, but the subsequent separation of thedesired component is often the most involvedprocess!


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Separations Why Design?

The first goal in separation design is to obtain therequired products from the given feeds.

The second goal is to minimize the cost of theequipment that is design it such that it works, butalso such that it is not oversized or undersized thus,minimizing construction costs and problems.

The third goal is to minimize operating costs sinceseparations, such as distillation the most commonseparation method consume enormous amounts ofenergy, often up to 50% of a plants operating costs.


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Mechanisms of Separation

One takes advantage of differences in thechemical and physical properties ofchemical species to enable their separation

these differences can involve theirmolecular, thermodynamic, and transportproperties.

If these differences are not significantly

large at given conditions, one may increasethe magnitude of these differences byaltering the system conditions or by theaddition of other species.


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Separation viaThermodynamic Properties

One of the most powerful differences that wecan take advantage of for separation is thedifferences in the thermodynamic properties ofdifferent chemical species.

The thermodynamic properties of the chemicalspecies can be altered by changes in the system

temperature and pressure, which often can bereadily and relatively easily varied in a process.


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What thermodynamic properties?

The relative volatility of chemical species ata particular temperature and pressure is oneof the most useful thermodynamic

properties for separation.Volatility is the tendency of a chemical

species to vaporize to a gas; thus, it isrelated to its boiling point.

Most chemical species have a differentvolatility or boiling point than others.


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Vapor-Liquid Phase Separations If a mixture of components is

allowed to separate into vapor andliquid phases, the more volatilecomponent the one with the lowerboiling point will tend to be morehighly concentrated in the vaporphase.

If we then separate the vapor fromthe liquid, we have increased theconcentration of the component inthe vapor phase with respect to theliquid phase.

The separation of the vapor fromthe liquid is readily accomplished by

their differences in density avapor phase comes of the top andthe liquid phase off the bottom ofthe separator.

It is that simple! Except that


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Equilibrium The Determining Separation Factor

The ultimate concentrations of the chemical specieswith respect to the phases are determined bythermodynamic equilibrium for a given set ofconditions.

Given the temperature, pressure, and concentrationsof a mixture, we can use equilibrium relationships todetermine the liquid and vapor phase concentrations ofthe chemical species as they separate.

By assuming equilibrium in our separation designs, wecan thus solve design problems.


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Staged Separations

Equilibrium is the determining factor as to what concentrations canbe obtained in the liquid and vapor phases at a given set ofconditions.

Equilibrium behavior, and thus the concentrations in the liquid andvapor phases, can be changed by altering the conditions of the

system for example, the temperature and/or pressure.

Multiple separations may be employed in series, each at differentconditions, to take advantage of even slight differences in theequilibrium concentrations to ultimately obtain high levels ofseparation.

Each separator can be thought of as an equilibrium stage in theoverall separation.

We can even combine these stages into an overall singleseparator, as we will see, for example, in distillation.


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So what is this course about?

We will use equilibrium relationships to determine thevapor and liquid behavior of mixtures of chemical speciesas they separate.

We will use this behavior in conjunction with mass andenergy balances to solve separation problems.

We will incorporate staged separations to achieve thedesired level of separation.

We will design separators using all of the above.


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Separations Design


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End of Lecture 1

lecture01 week 01

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